The vertebrate pancreas has two glands: exocrine acini and pancreatic ducts comprise the exocrine pancreas, which secretes and transports digestive enzymes to the duodenum; four types of endocrine cells ( 13,5, and PP cells) form endocrine islets of Langerhans, which secrete endocrine hormones to regulate a variety of physiological processes. Disease related to the pancreas includes pancreatic cancer, one of the leading causes of cancer death, and diabetes mellitus, which afflicts over 16 million individuals in the United States. As a result, pancreas-related studies not only shed light on the basic mechanisms that direct organogenesis, but also bear strong implications for human health. Despite the increased efforts and rapid progress in elucidating the molecular and cellular mechanisms underlying pancreatic development, little is known about the regulatory interactions that lead to pancreatic cell differentiation. For example, although it is known that Notch signaling participates in endocrine-exocrine cell fate determination by controlling the expression of a basic loop-helix-loop protein, NGN3, it is not known what other factors cooperate with NGN3 to induce mature endocrine cell differentiation nor what factors are needed to maintain proper islet function. In order to address these questions, this principal investigator has successfully utilized a temporally controlled cell marking technique to identify progenitor cells for mature endocrine islets. We found that transient Ngn3 expression in the pancreatic buds marks endocrine progenitor cells. Isolation of the Ngn3-expressing cells by GFP tagging and examination of their gene expression profiles using microarray-based analysis has revealed several candidate genes that may play roles in endocrine development. Our preliminary data indicate that the products of one of these candidate genes, myelin transcription factor I (Mytl, which produces two MYT1 isoforms), potentially interact with NGN3 and are involved in endocrine differentiation. In this proposal, we will first develop MYT 1 peptide antibodies to extensively study Mytl expression in the pancreas at different stages. Then we will utilize a temporally controlled gain-of-function approach to investigate the hypothesis that MYT1 provides competence to pancreatic cells to differentiate to mature islet cells in response to NGN3. Specifically, we will co-express Mytl and Ngn3 in pancreatic cells at different stages to determine whether they cooperate to induce islet cell maturation. In addition, loss of function approaches, including siRNA or knockout, will be utilized to selectively inactivate Mytl at embryonic or adult stages to [unreadable] examine its function for endocrine development and function. These fundamental studies not only identify molecular cascades for organogenesis, but also reveal crucial factors that can be used to induce endocrine differentiation or regeneration, so that functional islet ceils can be induced for relief of diabetic symptoms. [unreadable] [unreadable]